Without a connection to the internet, it can't deliver search results, provide turn-by-turn directions, instantly share pictures with friends, or accomplish any of the other feats promised in Google's video demonstration of Glass.

And yet Google Glass lacks the ability to connect to a cellular network on its own. It can only access one through a wireless Bluetooth connection to the wearer's cell phone. The question is: why?

The answer to that question is almost certainly that cellular radios simply draw too much power. Getting decent battery life out of a cell-connected Google Glass would probably require that it become Google Safety Goggles, with a battery pack attached to the strap running around the back of the wearer's head.

But there's a second reason that Google and every other maker of forthcoming face-based systems probably shouldn't even attempt to turn smart glasses into cell phones: They could become the definitive test of whether or not cell phones cause cancer, and not in a good way.

Public health professionals will tell you two things about this issue: First, whether or not cell phone use elevates levels of cancer is controversial—there have been multiple conflicting studies on the issue. So, second, we simply don't know if the radio frequency radiation pouring out of our phones has any measurable effect on us. The World Health Organization classifies radio-frequency fields as "possibly carcinogenic to humans."

But the US Federal Communications Commission certainly has opinions on the matter. It has guidelines for phone makers that describe the limits to how much radio frequency energy the human body should be allowed to absorb. As Quartz reader and software developer Brian Topping pointed out in response to our recent piece on the Neptune smartphone watch, any object that attaches a cell phone radio to a specific place on the wearer's body, day after day, is going to deliver point levels of radio frequency radiation that could run afoul of the FCC's rules. (We've reached out to Google about whether or not this came up as it worked on Google Glass, and will update with what we hear back.)

The FCC's rules could be one reason why the data on cancer and cell phones is so mixed—regulators stepped in to keep our phones from becoming lethal. But attaching a cell radio to a specific point on your skull or your wrist and wearing it all day, every day? Probably not a good idea.